This invention relates to rotating pumps or compressors of the scroll type, and is more particularly directed to an improved construction involving an integral shaft and counterweight.
Scroll type compressors have been known, in principle, for several decades In general, a scroll-type compressor or similar machine comprises a pair of mating scrolls, each of which has an involute spiral wrap of similar shape, mounted on respective base plates. Normally, one scroll is held fixed, and the other is orbited to revolve, but not rotate, being held by an Oldham ring or other anti-rotating structure. The walls of the two involute wraps define crescent-shaped volumes which become smaller and smaller and move from the outside to the center of the mating scrolls as the orbiting scroll revolves. A compressible fluid, such as a refrigerant gas, can be introduced at the periphery of the spiral wraps, and is compressed as it is moved under the orbiting motion of the device. The compressed fluid is then discharged at the center. By introducing a compressed fluid at the center and permitting its expansion to drive the device, the scroll machine can be used as a motor.
However, the orbiting motion of the moving scroll is unbalanced and off axis. Consequently, a moment is involved, which must be appropriately balanced by a suitable counterweight. Current designs for scroll-type compressors or other scroll-type rotating machines are rotationally supported on the rotor shaft between the position of the rotor and the eccentric drive for the orbiting scroll. This requires that the counterweight be positioned a considerable axial distance away from the orbiting scroll that it is intended to counterbalance. Often, the counterweight is attached onto the rotor, and a bearing for the shaft has to be designed to accommodate the rotor-mounted counterweight.
Where the counterweight is a separate part that must be attached to the rotor or shaft, an additional assembly step is required. Also, the counterweight can possibly become loose under severe use or after prolonged operation, thus limiting the reliability of the compressor.